This invention relates to an improved coaxial cable design and, more particularly, the invention is concerned with providing a coaxial pulse transmission cable wherein the sheath self inductance and the sheath to inner conductor mutual inductance are maintained near equality in order to cancel transient voltage on the sheath when the cable is pulsed.
When a coaxial cable is used for high voltage pulse transmission, a transient voltage appears on the outer sheath conductor. Although the magnitude of the transient is in the order of only a few percent, this amounts to several kilovolts in many cases and must be carefully considered in terms of its effect on instrumentation, control and safety.
To a first approximation, theoretically a coaxial cable should not develop any voltage on the outer sheath. A more refined analysis shows that the complete cancellation depends upon the self inductance of the sheath being exactly equal to the mutual inductance between the sheath and the center conductor. This condition is never satisfied due to current distribution effects, even when the distribution is uniform and radially symmetric. The situation becomes worse when proximity effects are accounted for.